Documents suddenly become "Read only" - what gives?

I have had two cases today where a document suddenly became read only or I couldn't open it at all because I supposedly didn't have the right permissions.

Trying to figure out what is going on.

I'm on 10.11.5

First document was a two page pdf.
Comes up that it can't be opened because I don't have the right permissions.
The pdf was on my Mac, I had looked at it before, so don't know why there would suddenly be a problem.
Checked Info and it shows that I have read & write permissions.
I changed that to read only, then back to read & write, but that made no difference.
The problem seems to be just with Preview - when I tried to open the pdf with either Acrobat 9 or Acrobat Reader - worked with either one.

The second problem was with an Excel spreadsheet I just updated.
Comes back with the message that I can't update it - to update it I need to assign a different name.
Saved the changes as "untitled" that worked fine.
But then I thought of any changes - I had changed the name of the spreadsheet and added p/o (as in part of).
Turns out if I delete p/o from the name I can update and save it just fine.
Is the Mac OS getting confused because of the "/"?

via ehMac.ca http://ift.tt/2jFIORU